Three days after three Muslim students were murdered by a neighbor near the University of North Carolina Chapel Hill campus, the FBI has opened a "preliminary inquiry" into the case. Federal officials are helping collect evidence alongside local authorities in the search for a motive behind the slayings of married students Deah Barakat, 23, and Yusor Abu-Salha, 21, and Yusor's 19-year-old sister, Razan Abu-Salha.

According to NBC News, the families of the three students believe that they may have been killed because they were Muslim, but, so far, local police have said it appears a parking dispute with neighbor Craig Stephen Hicks, 46, at the off-campus apartment complex where the three were murdered may have spurred the crime.

"The FBI has also opened a parallel preliminary inquiry to determine whether or not any federal laws were violated related to the case," the Bureau said in a statement. The initial probe is just short of a full investigation, but in the meantime, Hicks has been charged with three counts of first-degree murder.

Chapel Hill police chief Chris Blue said the investigation has suggested that the crime was "motivated by an ongoing neighbor dispute over parking," and Hicks' wife has denied that he harbored anti-Muslim sentiment. The families of the three students, however, believe it was a hate crime and have said they complained about aggressive behavior from Hicks in the past.

CNN reported that neighbors described Durham Technical Community College paralegal student Hicks as someone who was known for angrily confronting neighbors over loud music and parking issues and at one point last year it got so bad that a group of neighbors organized a meeting "to talk about how he kind of made everyone feel uncomfortable and unsafe."

Dr. Mohammad Yousif Abu-Salha, whose daughters were killed, was adamant that there was more to it than parking. "We have no doubt that the way they looked and the way they believed had something to do with this," he said.

Thousands mourn at funerals for Deah, Yusor and Razan

Anadolu Agency

Under grey skies on Thursday, more than 5,000 people gathered in Raleigh for the funerals of the three victims, with crowds so large the service had to be moved from the local mosque to a nearby athletic field on the campus of North Carolina State University, where Razan was a student.

"Everyone looked up to them and you can tell everyone loved them and they were loved and so kind and generous," Kawther Asad, who attended the funeral and knew the victims told the Daily Tarheel. "Everything about them was amazing... Everyone here should just use them as role models and try to live up to what they were and let their legacy live on."

The three, all of Syrian descent and known for their charitable work in the local community and abroad, should be remembered for their peaceful natures, said Dr. Abu-Salha at the funeral, according to USA Today. "When we say this was a hate crime it is all about protecting all other children in the USA... It's all about making this country that they loved, where they lived and died, peaceful for everybody else."

Thursday night also saw prayer vigils in honor of the three all across the country, including a large one in Washington, D.C.